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A Monte Carlo Study of Dosimetric Impact of Gadolinium Contrast Medium in Transverse Field MRI-Linac

T Kubota*, F Araki , T Ohno , Kumamoto University, Kumamoto, 43


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To investigate the dosimetric impact of gadolinium contrast medium (Gadovist) in transverse field MR-Linac using Monte Carlo calculations.

Methods: First, the dose distributions under the magnetic fields of 0-3.0 T were calculated using a virtual heterogeneous multi-layer phantom consisted of Gadovist and water using the EGSnrc/DOSXYZnrc code. The concentration of Gadovist was 0.05-1.0 mmol/mL which is commercial concentration. A 7 MV photon beam was irradiated with a 5 × 5 cm² field using the published Elekta MR-Linac spectrum. Next, dose distributions for patients with brain-VMAT and head and neck (H&N)-IMRT in 0-3.0 T were calculated with and without replacing the gross tumor volume (GTV) with Gadovist. Two plans were created by a treatment planning system. The prescription doses for brain and H&N tumors were 85% of 48.9 Gy and 50 Gy for D₉₅ in the PTV, respectively. The dose distributions under the magnetic fields of 0-3.0 T were calculated using EGSnrc/BEAMnrc and DOSXYZnrc codes. The dose distributions were analyzed by dose volume histograms, dose differences, and dose indices.

Results: The dose at the water-Gadovist interface increased by 8% without magnetic field. The similar dose increase was observed at 0.35 T. Reversely, the dose increase at the water-Gadovist interface decreased by 3% at 1.5 T and by 5% at 3.0 T. For brain tumor, D�m₎ₑ��n₎ in GTV with Gadovist increased by 6.6%, 2.6%, 3.6%, and 2.7% at 0, 0.35, 1.5, and 3.0 T compared to that of GTV without replacing, respectively. For H&N tumor, D₉₅ and D�m₎ₑ��n₎ in GTV with Gadovist increased by 6.2-7.5% and 4.7-5.4% at 0-3.0 T compared to those of GTV without replacing, respectively.

Conclusion: The dosimetric impact of Gadovist changed depending on the magnetic field strength. Consequently, Gadovist was useful for not only the image contrast enhancement but also the dose enhancement in transverse MRI-Linac.


Magnetic Fields, Monte Carlo, Dose


TH- External beam- photons: Monte Carlo

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